• The compounds possessing identical molecular formula but different structures are called isomers. Various types of isomerism 1. Structural isomerism 2. Stereoisomerism Stereoisomerism • Same molecular formula and same structure but they differ in configuration. • That is arrangement of their atoms in space. • Presence of asymmetric carbon atoms allow the formation of stereoisomerism

1. Carbohydrate chemistry II
Structure and Isomerism
Dr. Vijay Marakala, MD.
Assistant professor
BIOCHEMISTRY
SIMS & RC

2. Structure of monosaccharide
Fisher
projection
• The straight
chain structural
formula
Haworth
projection
• Cyclic formula
or ring
structure
X-ray
diffraction
analysis
• Boat and chair
form

3. Straight chain
Ring structure
Chair form

7. Isomerism
• The compounds possessing identical
molecular formula but different structures are
called isomers.
Various types of isomerism
1. Structural isomerism
2. Stereoisomerism

8. Structural isomerism
• Same molecular formulae but differ from each
other by having different structures.

9. Stereoisomerism
• Same molecular formula and same structure
but they differ in configuration.
• That is arrangement of their atoms in space.
• Presence of asymmetric carbon atoms allow
the formation of stereoisomerism

10. Stereoisomerism
• The important types of stereoisomerism
associated with glucose are
D and L isomerism
Optical isomerism
Epimerism
α and βanomerism

11. D and L isomerism

12. Optical isomerism
• Optical activity is the capacity of a substance
to rotate the plane polarized light passing
through it.
Clockwise direction
• Dextrorotatory(d) or (+)
Counterclockwise direction
• Levorotatory(l)or (-)

13. Optical isomerism

14. Epimerism
• Epimerism is the stereoisomerism if two
monosaccharides differ from each other in
their configuration around a single specific
carbon(other than anomeric) atom.

15. Epimerism

16. Anomerism
• These are isomers obtained from the change
of position of hydroxyl group attached to the
anomeric carbon e.g. and glucose are 2
anomers.
• Also and fructose are 2 anomers.

17. Anomerism

18. • Mutarotaion is defined as the change in the
specific optical rotation by the interconversion
of α and β forms of D glucose to an
equilibrium mixture
Mutarotaion

19. Structure of oligosaccharides
• Disaccharides
Disaccharides
Reducing
Maltose
Lactose
Isomaltose
Nonreducing
Sucrose

20. DISACCHARIDES
• These are glycosides formed by the condensation of 2
simple sugars.
• If the glycosidic linkage involves the carbonyl groups of
both sugars ( ) the resulting disaccharide is
• On the other hand, if the glycosidic linkage involves the
carbonyl group of only one of the 2 sugars (as in maltose
and lactose) the resulting disaccharide is reducing.

26. POLYSACCHARIDES
• These are formed by the condensation of n molecules of
monosaccharides with the removal of n-1 molecules of
water. Since condensation involves the carbonyl groups of
the sugars, leaving only one free carbonyl group at the end
of a big molecule, polysaccharides are non-reducing.
• They are of 2 types:
1. Homopolysaccharides (e.g. Starch, Glycogen, cellulose).
2. Heteropolysaccharides (e.g. glycosaminoglycans, glycoproteins)

29. - 1,4 linkage between
two glucose units
-1,6 linkage between
two glucose units

31. Aldehyde
group
H-C=O
Monosaccharides
Enantiomers
Mirror images of
each other
Disaccharides
sucrose = glucose + fructose
Lactose = galactose + glucose
Maltose = glucose + glucose
Oligosaccharides Polysaccharides
Homo-
Starch, glycogen,
cellulose
Hetero-
GAGs
Epimers
Differ in
configuration
around one
specific carbon
atom
Isomers
Same
chemical
formula
Ketoses
Keto
group
C=O
Aldoses